Magnetic self-latching pressure switch

ABSTRACT

A pressure-operated switch is provided that will maintain closure indefinitely until it is reset electrically. A permanent magnet is positioned close to a reed relay switch in response to a shock wave and the magnet acting in conjunction with two pole pieces effects the closing of the switch which then remains closed even when the shock wave no longer exists. The switch may then be reset to an open position by means of an electrical coil encompassing the reed switch.

United States Patent [191 Glass [111 3,824,512 [451 July 16, 1974MAGNETIC SELF-LATCHING PRESSURE SWITCH Inventor: Floyd M. Glass, OakRidge, Tenn.

The United States of America as represented by the United States AtomicEnergy Commission, Washington, DC.

Filed: Nov. 14, 1973 App]. No.: 415,912

Assignee:

US. Cl. 335/205, 200/83 L, 335/153 Int. Cl. .Q H0lh 35/32 Field ofSearch 335/ 153, 205-207;

References Cited UNITED STATES PATENTS Mathisen 200/83 L 3,349,203l0/l967 Wolford ..335/205X Primary Examiner-R. N. Envall Attorney,Agent, or Firm-John A. Horan; David S. Zachry; Louis M. Deckelmann [5 7]ABSTRACT A pressure-operated switch is provided that will maintainclosure indefinitely until it is reset electrically. A permanent magnetis positioned close to a reed relay switch in response to a shock waveand the magnet acting in conjunction with two pole pieces effects theclosing of the switch which then remains closed even when the shock waveno longer exists. The switch may then be reset to an open position bymeans of an electrical coil encompassing the reed switch.

3 Claims, 2 Drawing Figures 1 MAGNETIC SELF-LATCHING PRESSURE SWITCHBACKGROUND OF THE INVENTION This invention was made in the course of, orunder, a contract with the United States Atomic Energy Commission, and acontract with the Defense Civil Preparedness Agency.

An engineering feasibility study on automated attack-effects informationsystems was recently prepared at the Oak Ridge National Laboratory forthe Defense Civil Preparedness Agency. In this study, a pressure switchresponsive to an overpressure condution due to a shock wave was desiredthat would respond positively (switch closed) when interrogated,regardless of whether or not the overpressure was still present, andthat could be remotely resettable to a switch open position after beinginterrogated.

It is not common in the prior art to utilize a reed relay that isactuated to a switch closing position by a shock wave, and remainsclosed after the shock wave passes. Thus, there exists a need for apressure-operated switch that when closed in response to an overpressurewill remain closed even when the pressure condition no longer exists,and that can be remotely reset. The present invention was conceived tomeet this need in a manner to be described hereinbelow.

SUMMARY OF THE INVENTION It is the object of the present invention toprovide a magnetic self-latching pressure switch that will maintainclosure indefinitely until it is reset electrically.

The above object has been accomplished in the present invention byproviding a reed relay switch enclosed within a housing provided with abase, a nonmagnetic bellows attached to the base and forming the sidewalls of the housing, and a nonmagnetic diaphragm cover affixed to thetop of the bellows. A small permanent magnet is attached to the innerside of the diaphragm cover, and two low retentivity pole pieces areattached to opposite wire leads from the reed relay switch and arelocated a small distance from the magnet. When the magnet is movedcloser to the pole pieces in response to an overpressure force on thediaphragm cover, the resulting magnetic forces inducedin the pole pieceseffect a closing of the reed switch. Once closed, there is sufficientmagnetic flux in the pole pieces to maintain closure of the switch evenafter the passing of the overpressure force and the return of the magnetto its former position. When it is desired to reset the switch, this maybe accomplished by means of a simple electrical coil encompassing thereed switch which coil may be energized from a remote location if suchis desired.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top view, partially cutaway, of the pressure switch of the present invention.

FIG. 2 is a partial cross-sectional side view of the switch of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT 2. The reed switch 19 is notshown in FIG. 2 for the sake of clarity. The switching contacts of thereed switch 19 are connected to respective leads 17 and 18. A smallpermenent magnet 23 is attached to the inner side of the diaphragm cover15 and two low retentivity (soft iron) L-shaped pole pieces 21 and 22are attached, respectively, to the wire leads l7 and I8 and are locatedasmall (calibrated) distance from the magnet 23 in the manner shown. Thepole pieces 21 and 22 are supported, respectively, by posts 26 and 26mounted on the base 24.

In the operation of the above device, when it is subjected to anoverpressure force (e.g., a shock wave from an explosion), the diaphragm15 moves inward toward the pole piece 21, 22 as the bellows 16 absorbsthe force of the shock wave. The magnetic forces induced in the polepieces by the approaching magnet 23 have sufficient magnetic couplingthrough the leads 17 and 18 to close the reeds of the relay switch 19.When the switch closes, one (C) of the three air gaps (A, B, C) in themagnetic circuit is removed. This leaves sufficient magnetic flux tomaintain closure of'the reeds after the passing of the shock wave andthe return of the magnet 23 to its former position.

Thus, when one or more of the pressure responsive switches of thepresent invention are located at each of a plurality of separated sensorstations, then each of the switches can be interrogated by externalcircuitry, not shown, in a sequential manner to determine which one orones of these switches has or have been closed in response to a shockwave.

The reed relay switch 19 of FIG. 1 is provided with an electrical coil20 encompassing the switch as shown in the drawing. This coil is adaptedto be connected by means of suitable leads to an external power supplyby means of a remote control switch, all not shown. Thus,

' after the pressure switch 19 has been interrogated and has been foundto be closed as a result of an overpressure or shock wave, then it maybe reset to an open condition by means of the coil 20 when it isenergized by momentarily closing the power supply circuit thereto.

Since the sensor, described above, must adjust to changes in atmosphericpressure, a short length of capillary tubing 25 extends through the base24 of the sensor, as more clearly shown in FIG. 2, such that this willallow breathing" without interfering with the operation of the sensor.

It should be noted that the normal spacing between the magnet 23 and thepole pieces 21 and 22 can be set at a desired calibrated value such thata desired overpressure will actuate the switch. For example, when twopressure sensitive switches are required at each sensing station, thenone may be constructed to close at an overpressure of 0.5 psi and theother constructed to close at an overpressure of 5 psi.

This invention has been described by way of illustration rather than bylimitation and it should be apparent that it is equally applicable infields other than those described. For example, it may be used for thesensing of pressure excursions in any kind of gas or liquid line.

What is claimed is:

l. A magnetic self-latching pressure switch comprising a base member; anon-magnetic bellows mounted on said base and provided with anon-magnetic diaphragm cover over the open end of said bellows; a reedswitch mounted on said base member and within said bellows; said reedswitch having first and second electrical leads connected to respectivecontacts thereof; a permanent magnet mounted on the inside of said coverto move toward said base responsive'to incidence on said cover of apressure wave; and first and second L- shaped pole pieces mountedsymmetrically on said base with respect to said magnet, each of saidpole pieces being connected to a corresponding lead from said reedswitch to induce an attractive polarity in said leads and on said switchcontacts, thereby effecting a closing of said switch contacts uponmovement of said magnet a calibrated distance toward said pole pieces inresponse to'said pressure wave, the distance between said pole piecesand said magnet being such that sufficient magnetic flux existstherebetween to maintain said contacts supply.

3. The pressure switch set forth inclaim 2, and further including ashort length of capillary tubing extending through said base to providefor automatic adjustment to changes in atmospheric pressure.

1. A magnetic self-latching pressure switch comprising a base member; anon-magnetic bellows mounted on said base and provided with anon-magnetic diaphragm cover over the open end of said bellows; a reedswitch mounted on said base member and within said bellows; said reedswitch having first and second electrical leads connected to respectivecontacts thereof; a permanent magnet mounted on the inside of said coverto move toward said base responsive to incidence on said cover of apressure wave; and first and second L-shaped pole pieces mountedsymmetrically on said base with respect to said magnet, each of saidpole pieces being connected to a correSponding lead from said reedswitch to induce an attractive polarity in said leads and on said switchcontacts, thereby effecting a closing of said switch contacts uponmovement of said magnet a calibrated distance toward said pole pieces inresponse to said pressure wave, the distance between said pole piecesand said magnet being such that sufficient magnetic flux existstherebetween to maintain said contacts closed upon return of said magnetto its normal position.
 2. The pressure switch set forth in claim 1, andfurther including an electrical coil encompassing said reed switch, saidcoil adapted to be selectively connected to a remote external powersupply, whereby the contacts of said reed switch when closed may bereset to an open condition by an energization of said coil by said powersupply.
 3. The pressure switch set forth in claim 2, and furtherincluding a short length of capillary tubing extending through said baseto provide for automatic adjustment to changes in atmospheric pressure.